String string1 = "Hello !";
String string2 = "Arduino";
String stringSum = "anyvalue";

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  delay(5000);
  Serial.println(string1);
  Serial.println(string2);
  Serial.println(stringSum);

  Serial.println("#1");
  Serial.println(string1);
  Serial.println(string2);

  Serial.println("#2");
  stringSum = string1 + string2;
  Serial.println(stringSum);

  Serial.println("#3");
  Serial.println(string1 + "Cambodia.");

  Serial.println("#4");
  Serial.println(string1 + 12345);

  Serial.println("5");
  Serial.println(string1 + millis());

  Serial.println("#6");
  string1 += "Append Operator";
  Serial.println(string1);

  Serial.println("#7");
  string1 += 123;
  Serial.println(string1);
}

void loop() {
  // put your main code here, to run repeatedly:

}